A housing of an electronic device and a container for storing or transporting chemical substances such as chemicals are provided with a ventilation opening for reducing the atmospheric pressure (internal pressure) within the housing (container). A vent filter is provided at the ventilation opening so as to block contaminants that may enter from the outside, such as dust and water droplets. As one of such vent filters, there has been known a vent filter for hard disk drives (HDDs).
The vent filter requires the function of preventing contaminants present outside the housing from entering the housing, and particularly the HDD requires very high air cleanliness. For this reason, the vent filter needs to suppress the dust and the gas generated from the vent filter itself to low levels.
Currently available vent filters have the function of inhibiting not only dust but also gaseous contaminants from entering. For example, Patent Document 1 discloses a filter assembly including: a plastic housing having a gas passage therein; and a filter sheet (air-permeable membrane) capable of adsorbing gaseous contaminants. The gas passage in the plastic housing allows gas distribution between the breather opening (ventilation opening) and the air-permeable membrane.
In addition, Patent Document 2 discloses a vent filter having a layered structure of a double-sided pressure-sensitive adhesive tape, a gas adsorbent, and an air-permeable membrane. The vent filter has a diffusion flow path (gas passage) therein, and thereby has the same function as that of the vent filter of Patent Document 1. Patent Document 2 takes an example of the use of a porous PTFE membrane as an air-permeable material. In various plastics, PTFE is a material having the least amounts of dust and gas generation, because PTFE has high heat resistance and does not melt even at high temperatures.